Optical testing instrument.



0. HENKER. OPTICAL resume msmymem. 'AP'FLICATION FILED MAYIZIG, I915.

Paten ed-m. '30, 1915.

'Germany, have invented a new -with a deflecting so that two juxtaposed images are s'rirrns PATENT orrron.

o'r'ro nnnxnn or JEN'A, GERMANY, ASSIGNOR TO THE FIRM on cam. zn'rssfor JENA,

. GERMANY.

OPTICAL TESTING INSTRUMENT.

Specification of Letters Patent.

Patented Nov. 3,0, 1915 Application filed May 26, 1915. Serial No. 30,638.

T 0 all whom it may concern:

Be it known that I, O'r'ro Hnunnma citizen of the German Empire, residing tt Jena,

an Optical Testing Instrument, of which the following is a specification.

The invention relates to an apparatus for the determination of the curvatures of the cornea. The measuring principle underlying such apparatus consists, as is well known, in bringing beforethe eye to be examined an object of known size, for instance two marks at a known dist ace apart, and in determining the size of the virtual image formed of the said object by the surface of the cornea, which acts as a convex reflector. As the virtual .image is formed very approximately in the focal plane of the reflecting cornea surface, from the size ofv the object and of the image and the distance of the object fromthe eye with suflicient accuracy for practical purposes the focal length and thereby the radius of curvature of the cornea surface. The size of the virtual image is determined with the aid of a microscope, which receives the reflected rays and is provided between its objective and its ocular with a device, with the help of which the required size of the image can be translated into a directly measurable quantity.

The invention relates more particularly to apparatus, with which a measuring object of constant size is employed, and in which, for measuring the size of the virtual image, the microscope is fitted internally device, which deflects the ray pencils entering the microscope.- by a constant anglein such a manner that two'or more images of the measuring object are v formed, the said deflecting device be ng displaceable in the direction of the optical axis, so that the images visible in the microscope can also be displaced relatively to one another. 7

Most of the apparatus of thiskind, known up to the present, which usually have as a measuring object two fixed marks disposed at either side of the microscope, havea deflecting device, which divides the ray pencils entering the microscope into two parts, formed, the deflecting device being arranged in such a manner that the direction, in which one image appears to be displaced relatively to the-other, is parallel to the line connecting useful.

. These apparatus,

it is possible to calculate p with a stance concentrically axis, and in place of the deflecting devices known up to the'present a refracting the two fixed marks. When a measurement is being made with such an apparatus, the

twogimages presented to the observer are brought, by the deflecting device being displaced in the direction of the microscope axis, 1nto a certain position relatively to one another, for instance so that they just touch each other in the direction, in which they appear to be displaced relatively to one another. Hence the position of the deflecting device requlred gives a measure for the size of the virtual image to be determined and thus, if the distance of the from the eye be kept constant, a measure for the radius of curvature of the cornea. however, only allow of the radius of curvature being determined in each case in one lane, namely that meridian lane which 1s parallel to the direction, in which the two images visible in the'micro-,

scope are displaced relatively to one another.

For gaining an idea asv to the size of the radii of curvature in other meridian planes, a fresh measurement must be made for each meridian. It has, in the English patent specificat10n 26,747 of the year 1912, to provide the microscope double deflecting device, such that in both of two directions perpendicular to each other there are formed two adjacent images, preferablyin conjunction with a circularly shaped mark, so that, with one setting of theapparatus, the images of the mark may be brought in the two perpendicular directions for instance into contact and the radii of curvature be .thus' measured. When, however, the 'cornea surface to be examined is astigmatic, it is even then necessary, for determining the principal planes of curvature, to make ments' in different meridian planes.

In the apparatus according to tion there is used asmeasuring object a circularly shaped mark, which is fixed for in- With the microscope body is located in the path conical surface, the axis of which coincides with the axis'of the microscope. Such a conical refracting body may be supposed as having bee developed from a series .of sector-shaped, \circularly disposed retracting prisms, the planes of principal section of which all pass through'the microscope axis a series of measure of the rays, which 1s" 'bounded on at least one of itssides by a therefore, been suggested the invenand each of which defiec'tsthe image ofthe circular mark in the microscope {by an. equal amount. When the number of prisms in the circle becomes infinitely great, a conical refracting body results, which forms of the circular mark in the microscope an infinite number of images so to speak, which are disposed in a circle concentrically with the microscope axis and overlap each other. As a consequence of this no image in the true sense of the term results, but, according to the amount by which the rays are deflected, an annular or circular image surface, which has a caustic line both at its outer and at its inner circumference. These caustic lines are, according to the ratios of curvature of the cornea, curves, which have more or less I the form of circles concentric with the micro-- scope axis, and their shape shows at a glance the ratios of curvature in all meridians,'so that in the case of astigmatic cornea surfaces the direction of the principal planes of ourvature may be recognized straight away. The measurement is carried out in a similar manner as with known apparatus; in the case of a fixed microscope the conical refra'cting body is displaced in the direction of the optical axis, until in the meridian plane,

in which the curvature is to be determined,-

the opposite points of the caustic lines have a certain distance apart, preferably until the opposite points of the inner caustic line just coincide on this meridian. If the distance of the circular mark from the eye to be ex amined be kept always constant, the position of the refracting body thus ascertained is of itself a measure of the required radius of curvature. The retracting body may be combined with a scale, on which the size of the radius orthe corresponding power may be read off directly. 4 A

It is immaterial for the working of the apparatus, whether the conical surface is applied to the refracting body in the form of an ordinary cone or in the form ofa hollow cone. For obtaining a simple constructive form, 'in both cases the refracting body will be bounded on one side by the conical surface and on the other side by a plane, which is perpendicular to the microscope surface.

' In order to be able in the case of an astigmatically curved cornea to determine the direction of the axes in a simple manner, a fixed angular scale, which is concentric with the optical axis, may be appropriately lo cated in the objective image plane of the microscope along with a rotatable pointer adapted to read on it. A stroke following the direction of a diameter may be appropriately used as a pointer, such a stroke being, with an elliptical caustic line, as in the present case, most easily set in the direction of the great or of the small axis.

The apparatus may be particularly easily manipulated when it is so constructed that in each case the position of the displaceable refrecting body or the size itself of the corresponding radius of curvature may be read ofl m the ocular field of view. This may be done by fitting in the objective image plane 'on being displaced in'the direction of the optical axis, the image of the index to move along the scale, so that to each position of the mark-image there corresponds a certain position of the prism and hence of the refracting body.

The Invention is shown in the drawing by a constructional example, of which- Figure 1 represents a vertical longitudinal section of the whole apparatus and Fig. 2 a cross-section on line 22 of F ig. 1.

The main part of the apparatus is formed by a microscope, of which the objective is marked a and the ocular lenses 6 and 6 The objective a. is fixed by means of its mount a to a tube 0 the ocular is journaled by means of its mount 1) to a tube of somewhatgreater diameter 0 which is screwed to the tube 0 in such a manner as Hiflbe rotatable and yet axially undisplacea e.

In order'that the ocular may be easily rotated, its mount Z) is provided with a milled flange b 7 The whole rests in a-ring 0? surthe tube a on an extensible rounding stand d.-

Behind the objective (1 and mounted in a tubular piece 6, which is displaceable in the tube 0 there isa plane parallel glass plate e carrying on its front side a sighting mark e To the tubular piece 0 is fitted a bent tube f,-which reaches through a slot 0 of the. tube c and contains an incandescent electric lamp 7, which illuminates the glass plate e in the direction of its surface and thus renders the sighting markc visible to an eye looking through the objective a.

On the left-hand end of tube 0 there is fixed by meansof a hub casing g of U-sha ed cross-section, ,which has inside it a number of incandescent electric lamps h, which are arranged in a circle concentric to the microscope axis and can vbe supplied jointly with current from a plug k The casing g of the lamps h is covered on the side facing the objective at with a ring g made of ground glass and in front of g a ring-shaped free only a narrow annular slit- 9*.

mean diameter of the slit 9* is so chosen this ring is a metal cover 9 which leaves The with relation to the diameter of the circle, on which the lamps h are disposed,,that the slit appears brightly illuminated 'from a point on the microscope -axis lying at a short distance'in front of the objective.

Within the tube 035;. tubular piece 71 bearing a rack i may bedisplaced by means of a pinion i and milled disk if in the direction of the In croscope axis. The tubular piece a bears a glass body is, which is plane on one side and is'bounded on its other side by a conical surface 70 the aXis of which coincides'with the microscope axis. In a recess n the glass body In a small refracting prism 70 is cemented, the plane of principallsection of which passes through the microscope axis.

Behind the glass bed is and fixed to the casing is a plane para rear surface of which coincides with the objective image plane and which bears on this surface a degree scale m, which is concentric with the microscope axis and ex-- tends over the upper semicircle (Fig. 2), and a scale n. extending in the directionof,

the vertical diameter (Fig.

- the innersurface of the annular casing g and therefore also receives light from the incandescent lamps h.

- Fitted inside the part p there is a ground glass disk q, bearing on its upper side a transverse mark 9 and at its upper end there is a'collective lens 1' and, cemented to the latter, a reflecting prism s, which deflects the rays coming from the mark 9 toward the ocular. The collective lens 1* forms through the prism 70 an image of the mark g onthe scale a lying in the objective image plane.

Whenin'use, ward the eye to be examined placing the part 6, the mark 6 the apparatus is directed toand, by dismark on which .he fixes his gaze, is set in measurements and be determined in such a such a manner that the patient sees a sharp image of the mark l-ying in infinity. 'The dis'tance'of the apparatus from the eye to be examined should be the same for all manner that, the glass body is were 'not lel glass disk Z, the

on the glass. .plate a, which serves the patient as the there, the rays proceedin from the circular illuminated slit 9 an cornea surface. would be united by the ocular a in the ocular focal plane to an image of the luminous slit. In consequence of the inreflected at the v terposition of the glass body is there results instead of the actual image an' image surface having two caustic lines, which render the curvature of the examined cornea visir" ble in all meridians. By setting the mark 0 to the greatest or smallest diameter of a caustic line, in the case of an astigmatically curved, cornea surface the position of the planes of principal curvature may be read oil on the angular scale m. The size of the radius .of curvature ,of the cornea in a certain meridian is obtained by displacing by means of the milled'disk i the tubular piece 71 along with the glass body 70 until on the required meridian, to which the mark 0 .has been set, the opposite points of the inner caustic line coincide. As, when the lass body It is displaced, in consequence of the being moved along with it, the

prism 70 position of the image also varies, that the lens 1' formsof the fixed mark (1 on the scale a, the position at any moment of the glass body 70 and consequentl the corresponding radius of curvature in the ocular field of view may be read off on the scale n.

I claim:

1. In an optical testing instrument a circular mark, a microscope disposed within the saidmark and a refracting body fitted between the ocular and the objective of the said microscope so as to be displaceable in the direction of the microscope axis, the said refracting body being bounded on at least one side by a conical surface, the axis of which coincides with that of the microscope.

2. In an optlcal testing instrument a ciradapted to read on the said scale, a prism fixed to the said refracting body so that its plane of principal section always passes through the said scale and an optical arrangement adapted to form an image of the said indicating mark on the said scale through the said prism.

OTTO HENKEB.

its 

